As shown in FIG. 1A and FIG. 1B, a Gigabit Passive Optical Network (GPON) includes 3 components: Optical Line Terminal (OLT), Optical Distribution Unit (ODU), and either Optical Network Unit (ONU) or Optical Network Terminal (ONT). In FIG. 1A and FIG. 1B, the ODU is a passive optical splitter, which is a pure optical module not processing any electrical signal. The OLT is a module on the office's side, and the ONU/ONT is a module on the user's side. From the OLT to the ONU/ONT is downlink direction, and from the ONU/ONT to the OLT is uplink direction. As shown in FIG. 1A, the downlink data are transmitted in a continuously broadcasted manner by using the Time Division Multiplexing (TDM) technology. As Shown in FIG. 1B, the uplink data are transmitted in bursts by using the TDM technology, and a ranging process is required to avoid data collision at the same time.
The GPON system supports TDM service data transmission. The technology of TDM service transmission over the GPON is explained in ITU-T G.984.3. The procedure for TDM service transmission over the GPON in current technology is shown in FIG. 2: at the sending side, the TDM services are encapsulated into GPON Encapsulation Mode (GEM) packets, then processed by GPON TC (GTC) layer, and then transferred through optical fibers. At the receiving side, after the optical-to-electrical conversion and GTC layer processing for the received data by the optical fibers, the data are decapsulated from GEM packets and the original TDM service data are restored accordingly. This invention does not relate to GTC layer process and therefore the corresponding description is omitted here. The data transferred in downlink direction, from the OLT to the ONU/ONT, are processed as described above. The data transferred in the uplink direction, from ONU/ONT to OLT, are processed similarly.
In the aforesaid prior art, in the downlink direction, the TDM service data are firstly processed by the OLT, then received and processed by the ONU/ONT, and restored to the source TDM signal. In the above process, the GPON downlink services in running status will not be interrupted. However, for the GPON uplink services, if an ONU/ONT is added to a working GPON system, the OLT will need to perform a ranging process for the new ONU/ONT. During the ranging process, the rest ONU/ONTs are required to be interrupted to avoid data collisions. As a result, the rest ONU/ONTs' uplink services will be interrupted, and the uplink services in working-status, which includes TDM services, will be interrupted accordingly.